diff --git a/Packages/StrandImport/Sources/StrandImport/HealthWriteback.swift b/Packages/StrandImport/Sources/StrandImport/HealthWriteback.swift
index 5372f21c1b..ccd97af1fe 100644
--- a/Packages/StrandImport/Sources/StrandImport/HealthWriteback.swift
+++ b/Packages/StrandImport/Sources/StrandImport/HealthWriteback.swift
@@ -176,6 +176,49 @@ public enum HealthWriteback {
         "noop:\(kind):\(identity)"
     }
 
+    /// When each day's nightly vitals are stamped: the midpoint of the LONGEST night whose wake falls on
+    /// that day. `dayOf` maps a unix second to the day string the vitals rows are keyed by.
+    ///
+    /// Inside the night, not on its edge. The values are nightly aggregates, and a reader of Health picks
+    /// them by the sleep window they describe — Bevel shows no Recovery when HRV or resting HR is not
+    /// captured during the sleep window. A sample stamped exactly at wake sits on that boundary. The
+    /// longest night rather than the latest, so a nap after the main sleep does not carry the night's
+    /// values out of the night they came from.
+    ///
+    /// The midpoint of a bridged night can fall in the awake gap between its fragments, or in an awake
+    /// segment of one. It is still inside the `.inBed` sample, but a reader that keys off asleep samples
+    /// would not see it, so an instant that lands outside every asleep interval moves to the nearest
+    /// asleep second. A night whose stages carry no timing has only `.unspecified` asleep intervals and
+    /// keeps its midpoint.
+    public static func vitalsInstantByDay(_ entries: [MergedSleepEntry],
+                                          dayOf: (Int) -> String) -> [String: Int] {
+        var longest: [String: MergedSleepEntry] = [:]
+        for entry in entries where entry.spanEnd > entry.spanStart {
+            let day = dayOf(entry.spanEnd)
+            if let current = longest[day],
+               current.spanEnd - current.spanStart >= entry.spanEnd - entry.spanStart { continue }
+            longest[day] = entry
+        }
+        return longest.mapValues { entry in
+            let mid = entry.spanStart + (entry.spanEnd - entry.spanStart) / 2
+            let asleep = entry.intervals.filter { $0.kind != .awake && $0.end > $0.start }
+            if asleep.isEmpty || asleep.contains(where: { $0.start <= mid && mid < $0.end }) { return mid }
+            // Closest second inside each asleep interval; the nearest wins, the earlier on a tie. A plain loop:
+            // the equivalent `map { }.min { }` chain exceeded the type-checker's budget on CI.
+            var best = mid
+            var bestDistance = Int.max
+            for interval in asleep {
+                let candidate: Int = min(max(mid, interval.start), interval.end - 1)
+                let distance: Int = abs(candidate - mid)
+                if distance < bestDistance || (distance == bestDistance && candidate < best) {
+                    best = candidate
+                    bestDistance = distance
+                }
+            }
+            return best
+        }
+    }
+
     /// The vitals key: `noop:<metricId>:<day>`.
     public static func appleHealthVitalKey(metricId: String, day: String) -> String {
         appleHealthExternalUUID(kind: metricId, identity: day)
diff --git a/Packages/StrandImport/Tests/StrandImportTests/HealthWritebackTests.swift b/Packages/StrandImport/Tests/StrandImportTests/HealthWritebackTests.swift
index db0be640c3..e91b9cdabe 100644
--- a/Packages/StrandImport/Tests/StrandImportTests/HealthWritebackTests.swift
+++ b/Packages/StrandImport/Tests/StrandImportTests/HealthWritebackTests.swift
@@ -339,4 +339,56 @@ final class HealthWritebackTests: XCTestCase {
         swept = HealthWriteback.strandedSweepResult(swept: swept, succeededThisRun: ["sleepAnalysis"])
         XCTAssertEqual(swept, ["restingHeartRate", "sleepAnalysis"])
     }
+
+    // MARK: - Vitals stamp inside the night
+
+    private func entry(_ spanStart: Int, _ spanEnd: Int) -> HealthWriteback.MergedSleepEntry {
+        .init(keyStartTs: spanStart, spanStart: spanStart, spanEnd: spanEnd, intervals: [], allKeyStartTs: [spanStart])
+    }
+
+    /// Day = whole days since `start`, so attribution is by wake and independent of the test host's zone.
+    private func dayOf(_ ts: Int) -> String { "d\((ts - start) / 86_400)" }
+
+    func testVitalsAreStampedAtTheNightsMidpointNotItsWake() {
+        let night = entry(start, start + 8 * 3600)
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([night], dayOf: dayOf), ["d0": start + 4 * 3600])
+    }
+
+    /// A nap that wakes later the same day must not pull the night's values out of the night.
+    func testTheLongestNightOwnsTheDayNotTheLatest() {
+        let night = entry(start, start + 8 * 3600)
+        let nap = entry(start + 14 * 3600, start + 15 * 3600)
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([night, nap], dayOf: dayOf), ["d0": start + 4 * 3600])
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([nap, night], dayOf: dayOf), ["d0": start + 4 * 3600])
+    }
+
+    func testEachDayIsStampedByTheNightThatWokeOnIt() {
+        let first = entry(start, start + 8 * 3600)
+        let second = entry(start + 86_400, start + 86_400 + 6 * 3600)
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([first, second], dayOf: dayOf),
+                       ["d0": start + 4 * 3600, "d1": start + 86_400 + 3 * 3600])
+    }
+
+    /// A bridged night whose midpoint falls in the awake gap between fragments is stamped at the nearest
+    /// asleep second instead.
+    func testAMidpointInABridgedWakeGapMovesToTheNearestAsleepSecond() {
+        let bridged = HealthWriteback.MergedSleepEntry(
+            keyStartTs: start, spanStart: start, spanEnd: start + 8 * 3600,
+            intervals: [.init(start: start, end: start + 3 * 3600, kind: .light),
+                        .init(start: start + 3 * 3600, end: start + 4 * 3600 + 1800, kind: .awake),
+                        .init(start: start + 4 * 3600 + 1800, end: start + 8 * 3600, kind: .deep)],
+            allKeyStartTs: [start, start + 4 * 3600 + 1800])
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([bridged], dayOf: dayOf), ["d0": start + 4 * 3600 + 1800])
+    }
+
+    func testAMidpointInsideAnAsleepIntervalStays() {
+        let night = HealthWriteback.MergedSleepEntry(
+            keyStartTs: start, spanStart: start, spanEnd: start + 8 * 3600,
+            intervals: [.init(start: start, end: start + 8 * 3600, kind: .unspecified)], allKeyStartTs: [start])
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([night], dayOf: dayOf), ["d0": start + 4 * 3600])
+    }
+
+    func testANightWithNoSpanStampsNothing() {
+        XCTAssertEqual(HealthWriteback.vitalsInstantByDay([entry(start, start)], dayOf: dayOf), [:])
+    }
 }
diff --git a/StrandiOS/Health/HealthKitBridge.swift b/StrandiOS/Health/HealthKitBridge.swift
index bcb3b8bfab..dde5daa757 100644
--- a/StrandiOS/Health/HealthKitBridge.swift
+++ b/StrandiOS/Health/HealthKitBridge.swift
@@ -760,7 +760,7 @@ final class HealthKitBridge: ObservableObject {
 
     /// Write NOOP's strap-derived data into Apple Health: sleep sessions with full stage segments,
     /// the continuous 1-minute heart-rate stream, strap/manual workouts, and the nightly vitals
-    /// (resting HR, HRV, SpO₂, respiratory rate) stamped at that day's wake time.
+    /// (resting HR, HRV, SpO₂, respiratory rate) stamped at the midpoint of that day's night.
     ///
     /// Each feature saves independently and guards on ITS OWN type's share status, so one declined
     /// Health checkbox (or a save error) skips that feature without sinking the rest; the first error
@@ -780,7 +780,7 @@ final class HealthKitBridge: ObservableObject {
         let fromTs = Int(fromDate.timeIntervalSince1970)
         let nowTs = Int(now.timeIntervalSince1970)
 
-        // Sleep sessions drive both the sleep write and the vitals' wake-time stamps: computed
+        // Sleep sessions drive both the sleep write and the vitals' in-night stamps: computed
         // sessions (deviceId + "-noop") first, imported rows override on startTs collision — the
         // same source precedence as the dailies union below and IntelligenceEngine's sleep reads.
         let computedSleeps = (try? await whoopStore.sleepSessions(deviceId: computedDeviceId, from: fromTs, to: nowTs, limit: 200)) ?? []
@@ -878,21 +878,19 @@ final class HealthKitBridge: ObservableObject {
         }
     }
 
-    /// The nightly vitals write (the original write-back), now stamped at the day's wake time when
-    /// that day has a sleep session — a real timestamp inside the night the value describes, instead
-    /// of a fabricated noon. Keys are unchanged, so re-stamped samples replace their noon ancestors.
+    /// The nightly vitals write (the original write-back), stamped at the midpoint of the day's night
+    /// when it has one (`HealthWriteback.vitalsInstantByDay`) — a timestamp inside the night the value
+    /// describes, instead of a fabricated noon. Keys are unchanged, so re-stamped samples replace their
+    /// earlier wake- or noon-stamped ancestors.
     private func writeVitals(whoopStore: WhoopStore, days: Int, sessions: [CachedSleepSession]) async throws {
         let cal = Calendar.current
         let to = HealthKitBridge.dayString(Date())
         guard let fromDate = cal.date(byAdding: .day, value: -days, to: Date()) else { return }
         let from = HealthKitBridge.dayString(fromDate)
 
-        // day (of wake) → wake instant. Ascending session order means the latest wake of a day wins,
-        // matching collectSleep's end-date day attribution.
-        var wakeByDay: [String: Date] = [:]
-        for s in sessions where s.endTs > s.effectiveStartTs {
-            let wake = Date(timeIntervalSince1970: TimeInterval(s.endTs))
-            wakeByDay[HealthKitBridge.dayString(wake)] = wake
+        // day (of wake) → mid-night instant, attributed by wake like collectSleep's end-date attribution.
+        let instantByDay = HealthWriteback.vitalsInstantByDay(sleepPlan(sessions: sessions)) {
+            HealthKitBridge.dayString(Date(timeIntervalSince1970: TimeInterval($0)))
         }
         // Read NOOP's COMPUTED dailies (deviceId + "-noop"), which is the only place a strap-only
         // user's recovery/HRV/RHR/SpO₂/resp lives, then union with any imported `noopDeviceId` rows so
@@ -932,7 +930,7 @@ final class HealthKitBridge: ObservableObject {
         for row in rows {
             guard let date = HealthKitBridge.date(from: row.day) else { continue }
             let noon = cal.date(bySettingHour: 12, minute: 0, second: 0, of: date) ?? date
-            let at = wakeByDay[row.day] ?? noon
+            let at = instantByDay[row.day].map { Date(timeIntervalSince1970: TimeInterval($0)) } ?? noon
             if let rhr = row.restingHr {
                 add(.restingHeartRate, HKUnit.count().unitDivided(by: .minute()), Double(rhr), row.day, at)
             }
@@ -972,6 +970,21 @@ final class HealthKitBridge: ObservableObject {
         try await self.store.save(candidates.map { $0.sample })
     }
 
+    /// The bridged nights (#364) the write-back exports, shared by the sleep write and the vitals stamps so
+    /// both describe the same night.
+    private func sleepPlan(sessions: [CachedSleepSession]) -> [HealthWriteback.MergedSleepEntry] {
+        let blocks = sessions.map { SleepStageTotals.NightBlock(start: $0.effectiveStartTs, end: $0.endTs) }
+        let groups = SleepStageTotals.bridgedNightGroups(blocks, offsetSec: TimeZone.current.secondsFromGMT())
+            .map { g in
+                g.indices.map { i -> HealthWriteback.SleepFragment in
+                    let s = sessions[i]
+                    return .init(startTs: s.startTs, effectiveStartTs: s.effectiveStartTs,
+                                 endTs: s.endTs, stagesJSON: s.stagesJSON)
+                }
+            }
+        return HealthWriteback.mergedSleepPlan(groups: groups)
+    }
+
     /// Write each BRIDGED NIGHT (#364) as one `.inBed` sample plus one category sample per stage
     /// segment (`deep → .asleepDeep`, `rem → .asleepREM`, `light → .asleepCore`, `wake → .awake`) —
     /// the same shape Oura and Apple Watch write, so Health renders the full hypnogram. A night the
@@ -991,18 +1004,9 @@ final class HealthKitBridge: ObservableObject {
     private func writeSleep(sessions: [CachedSleepSession]) async throws {
         guard let type = HKObjectType.categoryType(forIdentifier: .sleepAnalysis),
               store.authorizationStatus(for: type) == .sharingAuthorized else { return }
-        let blocks = sessions.map { SleepStageTotals.NightBlock(start: $0.effectiveStartTs, end: $0.endTs) }
-        let groups = SleepStageTotals.bridgedNightGroups(blocks, offsetSec: TimeZone.current.secondsFromGMT())
-            .map { g in
-                g.indices.map { i -> HealthWriteback.SleepFragment in
-                    let s = sessions[i]
-                    return .init(startTs: s.startTs, effectiveStartTs: s.effectiveStartTs,
-                                 endTs: s.endTs, stagesJSON: s.stagesJSON)
-                }
-            }
         var samples: [HKCategorySample] = []
         var keys: [String] = []
-        for entry in HealthWriteback.mergedSleepPlan(groups: groups) {
+        for entry in sleepPlan(sessions: sessions) {
             let key = HealthWriteback.appleHealthSleepKey(startTs: entry.keyStartTs)
             let meta = [HKMetadataKeyExternalUUID: key]
             keys.append(contentsOf: entry.allKeyStartTs.map { HealthWriteback.appleHealthSleepKey(startTs: $0) })
diff --git a/Tools/parity_dispositions.json b/Tools/parity_dispositions.json
index 036071b6f1..da80dec35a 100644
--- a/Tools/parity_dispositions.json
+++ b/Tools/parity_dispositions.json
@@ -1,4 +1,13 @@
 {
   "schema_version": 1,
-  "dispositions": []
+  "dispositions": [
+    {
+      "type": "platform_specific",
+      "kind": "add-unpaired-function",
+      "identity": "swift\u0000Packages/StrandImport/Sources/StrandImport/HealthWriteback.swift::vitalsInstantByDay/2#1",
+      "identity_sha256": "cc1a46149abee1ead9df3a0da97441674f2ac5e5e966f178abd12b558bf24294",
+      "platform": "swift",
+      "rationale": "Used only by the iOS HealthKitBridge write-back to stamp nightly HKQuantitySamples inside the sleep window they describe; the Android Health Connect exporter does not call it."
+    }
+  ]
 }
diff --git a/Tools/parity_twin_map.json b/Tools/parity_twin_map.json
index 04df8ad57d..072a72268c 100644
--- a/Tools/parity_twin_map.json
+++ b/Tools/parity_twin_map.json
@@ -19,7 +19,7 @@
   },
   "authority": {
     "files": {"count": 500, "sha256": "515000556406ef31edcca8c0c5a5aae1c519e69b998e1920a30921b1d87cea57"},
-    "functions": {"count": 4449, "sha256": "1adfe3587fad29217a74fcfdd41629780744e18c8334684a7382411c3a55c6c6"},
+    "functions": {"count": 4450, "sha256": "7dbc2b2e19442915eb8b32d8bf7a4098946636f244c21d8420bc7eb460e146b3"},
     "properties": {"count": 458, "sha256": "d654302949fe0cb34f6e43a757e3a47fe485758e8a902c247285c0e288964d45"},
     "constants": {"count": 1943, "sha256": "28aef07e38b51398fa1f0b85c1d90415a12cf5d9923a582a38c0753cd2d451fd"},
     "file_pairs": {"count": 66, "sha256": "54ce5acd351bb1d2ce6bea06495cbfb7181975294ef7a94811e649be938f7f2a"},
@@ -27,7 +27,7 @@
     "property_pairs": {"count": 148, "sha256": "6fa59982fca9e8e306562b9d027676457c9fa4cc6766c1d6171e86084f3b2c54"},
     "constant_pairs": {"count": 676, "sha256": "e1e9dc35e152e5a439f1033e04a41ee28f5b6ea30cd8163746b67362ba0cdbed"},
     "unpaired_files": {"count": 386, "sha256": "19bf9fb79a6000964912b38eeeb61515ec0dfe7b8632e1d539dc29e537d61cc6"},
-    "unpaired_functions": {"count": 4109, "sha256": "a1c5691444fb06aa29ff47405d6fc673187efcc66acf6cbe31fbf318727b382f"},
+    "unpaired_functions": {"count": 4110, "sha256": "cfe8984f5fc1d61d65140f6e705682b70ce2784566864325e800fd66baa7b6ce"},
     "unpaired_properties": {"count": 162, "sha256": "eede893a804203b080f27bb05ca6a09ee9ac9d708ade984e2855813f35b6ae22"},
     "unpaired_constants": {"count": 591, "sha256": "c20942c8756be7c7c0bd38862eec53b1f0eb4ab25fbb68535d76d88d7b639514"}
   }